Amaury Balmer

For WordPress 2.3 and upper : Please try and use <a href="https://wordpress.org/extend/plugins/simple-tags/" title="The best tagging plugin for WordPress 2.3 !">Simple Tags Plugins</a>
The two mostly used tagging plugins are the Ultimate Tag Worrior (UTW) and Jerome’s Keywords.
I think most people use UTW, however especially its performance has been criticized in the past. Also, it does not provide a auto-complete type-ahead dropdown menu when tagging posts but it always displays all tags of the entire WordPress installation which can be quite annoying if you have really many tags.
Jerome’s Keywords is unfortunately still in beta and it seems that the project will not be continued.
With Simple Tagging Plugin, I’ve coded another tagging plugin for WordPress which is based on Jerome’s Keywords plugin and can ”’import”’ all your tags from UTW or Jerome.
It provides you with everything you need for tagging, in the following a list of the features:
<ol>
<li>Import your tags from UTW or Jerome’s Keywords</li>
<li>A field for tagging your posts easily incl. type-ahead feature</li>
<li>Display Tags of the current posts</li>
<li>A tag cloud with various options</li>
<li>Displaying a list of related posts</li>
<li>Related Tags feature when browsing your tags (idea stolen from del.icio.us)</li>
<li>Adding tags (& categories if enabled in the options) as meta keywords in the header</li>
<li>Adding tags as categories in the feed (this will index your tags with Technorati)</li>
<li>Tag management: rename tags, delete tags, replace tags, convert categories to tags, etc.</li>
<li>Support of embedded tags ([tags]tag1, tag2, tag3[/tags]): You can tag posts directly by entering the tags in the post using [tags]tag1, tag2, tag3[/tags]. This makes it possible to tag posts when you use an external blogging application like BlogDesk or Windows Live Writer.</li>
<li>A feed (RSS, RSS2, Atom) for any tag</li>
<li>Tag cloud for specific category</li>
<li>Automatically display the tags of a post after the post content</li>
<li>Generate Tag Tabs with jQuery !</li>
<li>Manage Tags Cloud in FULL WordPress Mu Site !</li>
<li>List posts from all blogs for a specific tags in WordPress Mu !</li>
<li>Edit mass tags ! 20 posts at the same time !</li>
</ol>
And more…
<h3>Arbitrary section</h3>
New in version 1.7: 
 * Reorganise Admin Options 
 * Add Tag Tabs 
 * Fix lots of bugs. 
 * Fix test $wp_version 
 * Atom Feed fix 
 * Add mass edit tags ! 
 * Fix a security problem
New in version 1.6.8.1: 
 * Fix a important bug with related posts
New in version 1.6.8: 
 * Fix bugs version 1.6.7 
 * Fix wrong counter tags 
 * Admin bugs. (checked) 
 * Minor optimisation 
 * Site wide tag cloud for WordPress Mu + List of posts. 
 * Add translation: Russian & Czech
New in version 1.6.7: 
 * Fix bugs version 1.6.6 
 * Compatibility with MySQL 4.0 
 * Optimisation
New in version 1.6.6: 
 * Add auto color tags cloud (no CSS, Colorpicker in admin) 
 * Add Turkish translation 
 * An option to limit the number of related tags 
 * A possibility to call/display the related posts outside a loop 
 * Tags Feed 
 * limit the age of what posts show up in the tag cloud 
 * An option to automatically display the tags of a post after the post content 
 * Limit or exclude category or categories in Tag Cloud 
 * Ability to exclude specific categories from the related posts 
 * Tag Cloud for one category
New in version 1.6.2: 
 * Related Posts now work…
New in version 1.6.1: 
 * Internationalisation (french, english, german) 
 * Compatibility with WPmu

Simple Tagging

For WordPress 2.3 and upper : Please try and use [Simple Tags Plugins](http://wordpress.org/extend/plugins/simple-tags/ "The best tagging plugin  …

Erick Hitter

Creates dropdown lists of non-hierarchical taxonomies (such as <code>post tags</code>) as an alternative to term (tag) clouds. Multiple widgets can be used, each with its own set of options.
Numerous formatting options are provided, including maximum numbers of terms, term order, truncating of term names, and more.
Using the <code>taxonomy_dropdown_widget()</code> function, users can generate dropdowns for use outside of the included widget.
Only use version 2.2 or higher with WordPress 4.2 and later releases. WordPress 4.2 changed how taxonomy information is stored in the database, which directly impacts this plugin’s include/exclude term functionality.
This plugin was formerly known as the <code>Tag Dropdown Widget</code>. It was completely rewritten for version 2.0.
Follow and contribute to development on GitHub at https://github.com/ethitter/Taxonomy-Dropdown-Widget.

Taxonomy Dropdown Widget

Creates a dropdown list of non-hierarchical taxonomies as an alternative to the term (tag) cloud. Formerly known as Tag Dropdown Widget.

Simple Tagging vs Taxonomy Dropdown Widget